diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index de4a6e8..24adff0 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -448,7 +448,7 @@
 
 #if defined(POLARSSL_SELF_TEST)
 
-static unsigned char entropy_source_pr[96] =
+static const unsigned char entropy_source_pr[96] =
     { 0xc1, 0x80, 0x81, 0xa6, 0x5d, 0x44, 0x02, 0x16,
       0x19, 0xb3, 0xf1, 0x80, 0xb1, 0xc9, 0x20, 0x02,
       0x6a, 0x54, 0x6f, 0x0c, 0x70, 0x81, 0x49, 0x8b,
@@ -462,7 +462,7 @@
       0x93, 0x92, 0xcf, 0xc5, 0x23, 0x12, 0xd5, 0x56,
       0x2c, 0x4a, 0x6e, 0xff, 0xdc, 0x10, 0xd0, 0x68 };
 
-static unsigned char entropy_source_nopr[64] =
+static const unsigned char entropy_source_nopr[64] =
     { 0x5a, 0x19, 0x4d, 0x5e, 0x2b, 0x31, 0x58, 0x14,
       0x54, 0xde, 0xf6, 0x75, 0xfb, 0x79, 0x58, 0xfe,
       0xc7, 0xdb, 0x87, 0x3e, 0x56, 0x89, 0xfc, 0x9d,
@@ -521,7 +521,7 @@
 
     test_offset = 0;
     CHK( ctr_drbg_init_entropy_len( &ctx, ctr_drbg_self_test_entropy,
-                                entropy_source_pr, nonce_pers_pr, 16, 32 ) );
+                                (void *) entropy_source_pr, nonce_pers_pr, 16, 32 ) );
     ctr_drbg_set_prediction_resistance( &ctx, CTR_DRBG_PR_ON );
     CHK( ctr_drbg_random( &ctx, buf, CTR_DRBG_BLOCKSIZE ) );
     CHK( ctr_drbg_random( &ctx, buf, CTR_DRBG_BLOCKSIZE ) );
@@ -538,7 +538,7 @@
 
     test_offset = 0;
     CHK( ctr_drbg_init_entropy_len( &ctx, ctr_drbg_self_test_entropy,
-                            entropy_source_nopr, nonce_pers_nopr, 16, 32 ) );
+                            (void *) entropy_source_nopr, nonce_pers_nopr, 16, 32 ) );
     CHK( ctr_drbg_random( &ctx, buf, 16 ) );
     CHK( ctr_drbg_reseed( &ctx, NULL, 0 ) );
     CHK( ctr_drbg_random( &ctx, buf, 16 ) );